Arterial hypertension no longer can be considered a single homogeneous disease. Hemodynamic characteristics, the fluid volumes, and participation of other pressor mechanisms (e.g., renin-angiotensin-aldosterone system, neural, endocrine, etc.) vary with different clinical forms and severity of disease. This proposal is designed to describe further the: systemic and regional hemodynamic characteristics, fluid volume partitions, renin-angiotensin-aldosterone system, and catecholamines in essential and secondary forms of hypertension of varying severity as they relate with one another. Since hemodynamic studies involve invasive procedures, they are most difficult to repeat frequently enough to obtain information about the natural course of the disease of therapy. We have developed methods whereby we can provide relatively inexpensive, reproducible, and noninvasive means for assessing systemic and regional hemodynamics in the ambulatory patient. Cardiac output (indicator-dilution) correlates well in patients with hypertension with simultaneously measured output by echocardiography; and we measure renal, hepatic, and forearm blood flows concurrently with output to understand target organ involvement associated with cardiac and vascular disease. Cardiovascular reflexive activity, using standard physiological maneuvers (e.g., upright tilting, Valsalva maneuver, isometric handgrip exercise, neck suction, isotonic exercise) will be measured at the time of hemodynamic studies. Operant conditioning effects (biofeedback) on hemodynamics, volume, and other pressor mechanisms will be evaluated. By studying secondary forms of hypertension (e.g., associated with diabetes mellitus, adrenal and hypercalcemic diseases, and oral contraceptives)--especially before and after correction of the underlying disorder--we will gain information regarding loss of pressure control induced by specific pressor mechanisms. With this multidisciplinary approach, we shall continue to be able to understand better the natural history of disease and to provide more specific therapy.